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Hydrates Calculator

Enter anhydrous molar mass and the number of water molecules to get hydrate molar mass and theoretical percent water.

Calculate Hydrate Composition

Enter the anhydrous salt molar mass and hydration number; add a sample mass if you also need grams of water and salt.

Hydrate molar mass, water percentage, and optional sample composition will appear here.

How to Use Hydrates Calculator

1

Enter the Anhydrous Molar Mass

Calculate or copy the salt molar mass without waters of hydration.

2

Enter the Hydration Number

For a formula ending in ·nH2O, enter n as a whole number.

3

Review Composition

Read hydrate molar mass and percent water; add sample mass for theoretical gram amounts.

Hydrates Calculator Features

  • Hydrate molar mass
  • Theoretical percent water
  • Optional sample composition
  • Transparent 18.015 g/mol water constant

Common Use Cases

Check a hydrate formula

Calculate the expected water percentage for an anhydrous salt with n waters of hydration.

Plan a chemistry sample calculation

Estimate grams of water and anhydrous salt in a theoretical sample.

Limits and Important Notes

Result type: Exact calculation

Calculation Details

  • Multiply the hydration number by 18.015 g/mol.
  • Add that water mass to the anhydrous molar mass.
  • Divide the water contribution by the hydrate molar mass and multiply by 100.

Formula

M(hydrate) = M(anhydrous) + n × 18.015; water % = n × 18.015 ÷ M(hydrate) × 100.

Rounding

Calculations retain floating-point precision; results display up to three decimal places.

Default Assumptions

  • The entered anhydrous molar mass is correct for the compound.
  • The hydrate has an integer number of water molecules per formula unit.
  • The theoretical sample contains only the named hydrate.

Verified Example

Inputs: CuSO4 molar mass 159.609 g/mol and n = 5.

Calculation: 159.609 + 5 × 18.015 = 249.684 g/mol; 90.075 ÷ 249.684 × 100.

Result: Hydrate molar mass 249.684 g/mol and about 36.075% water.

Sources and Version

Version: Water molar mass fixed at 18.015 g/mol

Last verified: 2026-08-18

Update responsibility: OnlineTool.me

  • The tool does not parse chemical formulas or look up atomic weights.
  • Experimental percent water may differ because of incomplete heating, decomposition, rehydration, or impurities.
  • Use the molar mass convention required by your course or laboratory.

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Frequently Asked Questions